common/iso15693tools.c

   1 //-----------------------------------------------------------------------------
   2 // This code is licensed to you under the terms of the GNU GPL, version 2 or,
   3 // at your option, any later version. See the LICENSE.txt file for the text of
   4 // the license.
   5 //-----------------------------------------------------------------------------
   6 // ISO15693 CRC & other commons
   7 //-----------------------------------------------------------------------------
   8
   9
  10 #include "iso15693tools.h"
  11
  12 #include <stddef.h>
  13 #include <stdint.h>
  14 #ifdef ON_DEVICE
  15 #include "printf.h"
  16 #else
  17 #include <stdio.h>
  18 #endif
  19
  20
  21 #define ISO15693_CRC_PRESET  (uint16_t)0xFFFF
  22 #define ISO15693_CRC_POLY    (uint16_t)0x8408
  23
  24
  25 // The CRC as described in ISO 15693-Part 3-Annex C
  26 //    v   buffer with data
  27 //    n   length
  28 //  returns crc as 16bit value
  29 uint16_t Iso15693Crc(uint8_t *v, int n) {
  30         uint32_t reg;
  31         int i, j;
  32
  33         reg = ISO15693_CRC_PRESET;
  34         for (i = 0; i < n; i++) {
  35                 reg = reg ^ ((uint32_t)v[i]);
  36                 for (j = 0; j < 8; j++) {
  37                         if (reg & 0x0001) {
  38                                 reg = (reg >> 1) ^ ISO15693_CRC_POLY;
  39                         } else {
  40                                 reg = (reg >> 1);
  41                         }
  42                 }
  43         }
  44
  45         return ~(uint16_t)(reg & 0xffff);
  46 }
  47
  48 // adds a CRC to a dataframe
  49 //    req[]   iso15963 frame without crc
  50 //    n       length without crc
  51 // returns the new length of the dataframe.
  52 int Iso15693AddCrc(uint8_t *req, int n) {
  53         uint16_t crc = Iso15693Crc(req, n);
  54         req[n] = crc & 0xff;
  55         req[n+1] = crc >> 8;
  56         return n + 2;
  57 }
  58
  59
  60 // returns a string representation of the UID
  61 // UID is transmitted and stored LSB first, displayed MSB first
  62 //    target    char* buffer, where to put the UID, if NULL a static buffer is returned
  63 //    uid[]     the UID in transmission order
  64 //    return:   ptr to string
  65 char* Iso15693sprintUID(char *target, uint8_t *uid) {
  66         static char tempbuf[2*8+1] = "";
  67         if (target == NULL) target = tempbuf;
  68         sprintf(target, "%02X%02X%02X%02X%02X%02X%02X%02X", uid[7], uid[6], uid[5], uid[4], uid[3], uid[2], uid[1], uid[0]);
  69         return target;
  70 }
  71
  72
  73 uint16_t iclass_crc16(uint8_t *data_p, unsigned short length) {
  74         unsigned char i;
  75         unsigned int data;
  76         uint16_t crc = ISO15693_CRC_PRESET;
  77
  78         if (length == 0)
  79                 return (~crc);
  80
  81         do {
  82                 for (i = 0, data = 0xff & *data_p++; i < 8; i++, data >>= 1) {
  83                         if ((crc & 0x0001) ^ (data & 0x0001))
  84                                 crc = (crc >> 1) ^ ISO15693_CRC_POLY;
  85                         else  crc >>= 1;
  86                 }
  87         } while (--length);
  88
  89         crc = ~crc;
  90         data = crc;
  91         crc = (crc << 8) | (data >> 8 & 0xff);
  92         crc = crc ^ 0x0BC3;
  93         return (crc);
  94 }
  95